The United Nations says that civilian casualties from fighting and insurgent attacks in Afghanistan have increased by nearly one-quarter in the first six months of this year.

The UN Assistance Mission in Afghanistan (UNAMA) said insurgent bomb attacks remained the biggest cause of civilian casualties, but increased ground fighting between Afghan government forces and militants was the second leading cause.

"The armed conflict brought increased suffering and harm to Afghan civilians in the first half of 2013," Georgette Gagnon, UNAMA's director for human rights, told reporters at a news conference in Kabul on July 31. "The number of civilians killed or injured rose by 23 percent compared to the same period last year."

The UNAMA report documented more than 1,300 civilian deaths and more than 2,500 injuries through June, up 23 percent from the same period last year.

It said 74 percent of civilian casualties were caused by insurgents, 9 percent by pro-government forces, and 12 percent resulted from "ground engagements" between insurgents and government forces. The remaining four or five percent were unattributed.

The report said more women and children had become victims of the 12-year-old war. The number of children killed over six months climbed 30 percent compared to the same period last year.

The UN also said insurgents were increasingly targeting civilians seen to be cooperating with the government.

UNAMA's Gagnon said the report was shared with all parties to the conflict a couple of days ago, including the Taliban.

"We are calling on all parties to the conflict, as is their legal obligation under international law, to exercise constant care to protect civilians from the dangers of military operations, in particular ground engagements, and to take all feasible measures to avoid and minimize civilian loss of life," Gagnon said.

Taliban militants increased attacks after Afghan government troops took the lead for security responsibility in the country from the NATO-led coalition. Most foreign troops are due to withdraw by the end of 2014.

The UN said that "despite Afghan forces leading almost all military operations countrywide," a permanent structure does not exist to "systematically investigate allegations of civilian casualties" and take follow-up action.

The International Security Assistance Force (ISAF) in a statement on July 31 reiterated its "untiring commitment to reduce civilian casualties." It also said "the Taliban's demonstrated lack of regard for human life has resulted in nearly 90 percent of all civilian casualties so far this year."

The Taliban rejected the UN report as "totally biased" and an "attempt of propaganda" against insurgents.